Preparation of fluorinated organic compounds



Patented Aug. 24, 1954 rFicE PREPARATION OF FLUORINATED ORGANICCOMPOUNDS Frank C. McGrew, Wilmington, DeL, and Edward H. Price, WestChester, Pa., assignors to E. I. du Pont de Nemours and Company,Wilmington, Del., a corporation of Delaware No Drawing. ApplicationFebruary 8, 1952, Serial No. 270,741

9 Claims. 1

This invention relates to the preparation of fiuorinated organiccompounds. More specifically, this invention relates to the preparationof fiuorinated methanes and fluoroethylenes by reaction between a loweraliphatic hydrocarbon compound and a chloro-fiuoro-methane.

The Benning et a1. patent, U. S. 2,551,573, discloses a pyrolysisprocess whereby a chlorofluoro-methane, preferably CHClFz, istransformed by heat alone into other fluorinated organic compounds, suchas tetrafluoroethylene. Such processes usually involvedehydrohalogenation, with the hydrogen and halogen atoms being splitfrom the same or different molecules of the same reactant. Startingmaterials containing hydrogen in the molecule, such as CHClFz, must beused in such prior art processes. Materials, such as CHClFz, have beendifficult and expen sive to obtain in the past.

An object of this invention is to produce monochlorodifluoromethane by aless expensive process than has been heretofore known. Another object isto produce 1,1-difluoroethylene by means of a process which is superiorto methods heretofore known. Other objects appear hereinafter.

The present invention employs a chlorodifiuoromethane as a startingmaterial. Chlorine is removed from the chlorodifluoromethane startingmaterial by reaction of a lower aliphatic hydrocarbon, such as methane,with the abovementioned starting material at a high temperature, in thepresence of a metallic catalyst, or without a catalyst, Such a reactionprobably produces free radicals such as -CI-I2 and -CF2- which combineto form an unsymmetrical difiuoroethylene. Removal of only one chlorineatom may also take place to produce CllIClFz, which is a valuablestarting material for the production of tetrafluoroethylene in theprocess described and claimed by Benning et 2.1., U. S. 2,551,573. Nolimitations on the scope of this invention are intended by postulatingany mechanism of the reaction.

In the preferred embodiment of the process of this invention,chlorodifiuoromethane and a lower aliphatic hydrocarbon are continuouslyintroduced, in the vapor phase, into a reactor that is maintained at atemperature from about 400 C. to about 1000 C. The reactant vapors areconverted to the desired products in the presence of metallic catalystscontaining platinum or copper. In the use of a platinum-containingcatalyst it is preferred to employ the catalyst in the physical form ofa gauze; while in the use of copper, it is preferred to employ thephysical form of turn..-

ings. The preferred chlorodifluoromethane is CClzFz, and the preferredlower aliphatic hydrocarbon is methane.

In the following examples various methods of producing CH2=CF2 andCHC1F2 by means of the process of this. invention are shown. Ihe gasvolumes are given in the examples in terms of cubic centimeters at roomtemperature (25 C.) and at one atmosphere absolute pressure. Thepressure inside the reactor tubes is, in the particular embodiments ofthis invention, less than about two atmospheres absolute pressure. Ineach of the examples the reaction tube is placed in an electric furnacewhich supplies the heat necessary to maintain the reaction temperaturefrom about 400 C. to about 1000 C. The reaction tube is sufficientlylong to extend beyond the furnace at either end, while the centralportion of the tube, 8% inches long, remains within the furnace and issubjected to the furnace heat. The contact times are calculated on thevolume of the hot zone of the reaction tube; the hot zone being definedas the space enclosed by the portion of the reaction tube which issubjected to the furnace heat. In all examples, the volume of the hotzone is the product of the internal cross-sectional area of the reactiontube and a length of 8% inches. The temperatures of the reacting gasespassing through the reaction tube are not uniform throughout the lengthof the tube. The non-uniformity of the temperatures may be due tovarious factors, such as (1) the heat of the reaction and (2) thetemperature gradient caused by the flow of mixed gases undergoingchemical reactions. The temperatures, therefore, are reported in theexamples as a range of temperatures which represent the fluctuations ofthe temperatures of the reacting gases in the hot zone. The productgases in each example are collected from the outlet of the reactor tube,cooled, scrubbed with aqueous alkali to remove acidic gases, such as HFand I-ICl, and are thus prepared for analysis.

Example I A quartz tube, 12 mm. inside diameter and 3 feet long, wasplaced in an electric furnace which produced sufficient heat to maintainthe temperature of the vapors in the tube at 720 to 760 C. The reactantvapors were fed into one end of the tube at the following rates:

CClzF'z cubic centimeters per minute" 200 CH4 do 196 This rate gave acontact time of 3.8 seconds.

The product contained the following relative mol proportions ofhalocarbons and halohydrocarbons Per cent CC12F2 89.0

CHC1F2 1.4 CHz=CF2 6 .8

CFsCl 1.4 Others 1.5

Example II The same equipment was used as described in Example I above.The temperature of the vapors inside the tube was maintained at 720 to760 C. The reactant vapors were fed into one end of the tube at thefollowing rates:

This example shows, by comparison to Example I, that with all otherconditions remaining the same, a lower feed rate, or higher contacttime, gives a higher concentration of the desired products, CHClFz andCH2=CF2.

Example III The same equipment was used as described in Example I above.The temperature of the vapors inside the tube was maintained at 770 to810 C. The reactant vapors were fed into one end of the tube at thefollowing rates:

CC12F2 cubic centimeters per minute 300 CH4 do 244 This rate gave acontact time of 2.7 seconds. The

product contained the following relative mol proportions of halocarbonsand halohydrocarbons:

Per cent CClzFz 75.1

CHClFz 3.7

CHz=CFz 16.5

CFsCl I..- 1.7

CH2 CHF 2.6 Others 0.5

Example IV The same equipment was used as described in Example I above,except thatv a. gauze made of 90% platinum-% rhodium alloy, 4. /2 inchessquare, was rolled loosely and placed in the center of the tube. Thetemperature of the vapors inside the tube was maintained at 720 to 760C. The reactant vapors were fed into one end of the reactor tube at thefollowing rates:

CClzFz cubic centimeters per minute 300 CH4 do 196 This rate gave acontact time of 3.0 seconds. The product contained the followingrelative mol proportions of halocarbons and halohydrocarbons:

Per cent CClzFz 92.3

CHClFz 2.3

Per cent CH2=CFz 3.8 CH2F2 0.9 CF3C1 0.8

Example V The same equipment was used as described in Example I above,except that a gauze made of platinum-10% rhodium alloy, 9 inches square,was rolled loosely and placed in the center of the tube. The temperatureof the vapors inside the tube was maintained at 770 to 810 C. Thereactant vapors were fed into one end of the reactor tube at thefollowing rates:

CClzFz cubio centimeters per minute 300 CH; do 244 This rate gave acontact time of 2.7 seconds. The product contained the followingrelative mol proportions of halocarbons and halohydrocarbons:

Per cent CC12F2 66.3 CF2=CF2 1.5 CHClFz 6.8

CH2=CFz 19.9 CF3C1 2.7

CH2=CHF 2.8

Example VI The same equipment was used as described in Example I, exceptthat a gauze made of 90% platinum-10% rhodium alloy, 4 inches square,was rolled loosely and placed in the center of the tube. The temperatureof the vapors inside the tube was maintained at 720 to 760 C. Thereactant vapors were fed into one end of the res actor tube at thefollowing rates:

CC12F2 cubic centimeters per minute 300 CH4 do 245 This rate gave acontact time of 2.7 seconds. The product contained the followingrelative mol proportions of halocarbons and halohydrocarbons:

Per cent CC12F2 9 6, .2 CHClFz 1.7 CH2=CF2 1.8 CFsCl 0.3

By comparing Example VI with Example V it can be seen that the use of acatalyst with larger sur-. face area, at a. higher temperature, hasincreased the concentration of CH2=CF2 tenfold and quadrupled theconcentration of CHClFz.

Example VII The same equipment was used as described in Example I above,except that ordinary copper turnings were packed loosely into the tubeso as to fill about 9 inches of the center of the tube. The temperatureof the vapors inside the tube was maintained at 670 to 720 C. Thereactant vapors were fed into one end of the reactor tube at thefollowing rates:

CClzF2 cubic centimenters per minute 300 CH4 do 196 This rate gave acontact time of 3.0 seconds. The product contained the followingrelative mol proportions of halocarbons and halohydr0carbons:

Per cent CC12F2 80.8

CHClFz 7.8 CH2=CF2 8.4 CH2F2 1.6, CFsCl V.. 1.4.

Example VIII The same equipment was used as described in Example Iabove, except that ordinary copper turnings were loosely packed insidethe tube so as to fill about 9 inches of the center of the tube. Thetemperature of the vapors inside the tube was maintained at 720 C. to760 C. The reactant vapors were fed into one end of the tube at thefollowing rates:

CC12F2 cubic centimeters per minute 300 CH4. do 244 This rate gave acontact time of 2.7 seconds. The product contained the followingrelative mol proportions of halocarbons and halohydrocarbons:

Per cent CClzFz 56.9

CF2=CFz 1.8

CHCIFz 11.0

CH2=CF2 19.2

CF3C1 4.4

CHz=CHF 5.6 Others 1.6

Emample IX The same equipment was used as described in Example I above,except that ordinary copper turnings were loosely packed inside the tubeso I as to fill about 9 inches of the center of the tube. Thetemperature of the vapors inside the tube was maintained at 675 to 715C. The reactant vapors were fed into one end of the tube at thefollowing rates:

CC12F2 cubic centimeters per minute 300 CH4 do 245 This rate gave acontact time of 2.7 seconds. The product contained the followingrelative mol proportions of halocarbons and halohydrocarbons:

Per cent CClzF'z 88.6 CF2=CF2 0.6

CI-IClFz 4.1 CH2=CF2 4.3

CH2F2 1.4

Others 1.0

Comparing this example to Example VII it can be seen that all variableswere kept constant, except that a lower temperature and a slightlyshorter contact time were used in Example VIII, causing lowerconversions to the desired products, CHClFz and CH2=CF2.

Example X The same equipment was used as described in Example I above.The temperature of the vapors inside the tube was maintained at 740 to790 C. The reactant Vapors were fed into one end of the tube at thefollowing rates:

CC12F2 cubic centimeters per minute 300 C2Hs do 241 This rate gave acontact time of 2.7 seconds. product contained the following relativemol proportions of halocarbons and halohydrocarbons:

' Per cent CClzFz -I 89.9 CH2=CFz 4 .3 CHClFz 2.8 CH2F2 1 .5

CFsCl 0.5

The

Ewample XI The same equipment was used as described in Example I above,except that ordinary copper turnings were looselypacked inside the tubeso as to fill about 9 inches of the center of the tube. The temperatureof the vapors inside the tube was maintained at 650 to 690 C. Thereactant vapors were introduced into one end of the tube at thefollowing rates:

CC12F2 cubic centimeters per minute 300 CzI-Ie do 243 This rate gave acontact time of 2.7 seconds. The product contained the followingrelative mol proportions of halocarbons and hydrocarbons:

Per cent CClzFz 88.4 CH2=CF2 4.1

CHClFz 5.4 CF2=CF2 0.8

CHzFz 1.0 CFsCl 0.3

It has been found that three of the variables of the invention may bechanged singly, or in com bination with each other, to give differingproduct yields. These three critical variables are: the temperature ofthe reactingvapors, the catalyst used, and the contact time for thereaction. In general, a higher temperature may increase the conversion,although extremely high temperatures may cause decomposition of theorganic vapors. The use of the catalyst in a physical form offering alarge surface area, such as a gauze or as turnings, will usually givegreater yields of the desired products. In addition, the metalliccatalysts, such as platinum alloy and copper, have been found to changethe proportion of CHClFz to CH2=CF2 in the products to a diiferentproportion from that obtained when no catalyst is used. Contact time,which is controlled by the feed rate, has been found to affect therelative proportions of the desired products. Thus, a shorter contacttime will, in general, give a lower production of CHClFz and CI-lz CFz,anda longer contact time will, in general, give a higher production ofCl-ICIF2 and CI-IzzCFz. A

comparison of the various examples recited will illustrate the effect ofchanging the temperature, catalyst, and contact time, either singly orin conjunction with another variable.

The operable limits of the temperatures of the reacting vapors have beenfound to be from about 400 C. to about 1000 C. Below 400 C. thereappears to be such a substantial decrease in con version that acommercial process is not feasible, even with longer contact times. .Atabout 1000 C. increasing decomposition and formation of less desirableproducts occurs as higher and higher temperatures are employed, with theresult that the process becomes impractical.

Metallic catalysts such as platinum alloy and copper give the bestresults and are preferred in the embodiment of the invention in which, acatalyst is used, although thisprocess is operable in the absence of acatalyst. Platinum alloy of platinum-10% rhodium has been shown in theexamples, however pure platinum and alloys of platinum with othermetals, such as, palladium, iridium, and others known to those skilledin the art, may be used in this process to obtain substantially the sameresults. Other catalysts that may be employed at lower temperatures togive lower yields are cooper-chromium oxides, cobalt oxides, nickeloxides and other hydrogenation catalysts familiar to those skilled inthis field.

One of the main advantages of this invention is the use of a loweraliphatic saturated hydrocarbon as one of the reactants. In processesheretofore used, all the carbon atoms in the products had to come fromthe halogenated alkane starting material. In the present inventioncarbon atoms are derived both from the halogenated alkane and from thehydrocarbon.

In the reaction of CH4 with CC12F2, 2 mols of HCl can theoretically beformed, and thus give rise to the probable formation of the radicals CF2and --CH2, one probably coming from CClzFz and the other probably comingfrom CH4. These two radicals could then reform to produce one of thedesired products, CH2=CF2. Since the cost of the starting materialsusually determines the cost of the product, this invention produces auseful polymerizable, fiuorinated olefin by a much cheaper process thanany other known at the present time, because of the fact that half ofthe carbon atoms have their source in methane, which is a larger, andmore widely available, source of supply than any halogenated methane.

Other hydrocarbons can be used as reactants in this invention. Ethane,propane, and butane can be used in place of methane, although slightlydifferent operating conditions are preferred to produce the desiredproducts. Methane is the hydrocarbon preferably used in this invention,although the process is not intended to be limited to theuse of methane,exclusive of other saturated aliphatic hydrocarbons.

The products of this invention are various chlorinated and fluorinatedmethane and ethylene derivatives, although longer chain derivatives canbe produced by using ethane, propane, and butane as reactants. The morevaluable components of the products of this process are CHC1F2 andCH2=CF2. CHClFz is a valuable intermediate to tetrafiuoroethylene. BothCHClFz and CH2=CF2 are valuable intermediates to solvents, variousmaterials employed as refrigerants, and other commercial chemicals.Vinylidene fluoride (CHa CFa) and vinyl fluoride (CI-IzzCHF), some ofthe latter also being produced in this process, are both valuable inthat they may each be polymerized to desirable polymeric products. It isparticularly advantageous that this process produces several halogenatedcompounds and that this process is flexible enough to allow control ofthe relative amounts of CHC1F2 and CH2 CF2 produced. By changing thevariables of temperature, catalyst, and contact time, the proportion ofCHClFz to CH2ICF2 can be increased or decreased, corresponding to thedegree of completeness with which this reaction is carried out.

The desired compounds can be separated from the product mixture byordinary methods of low temperature distillation and condensation knownto those skilled in the art. Yields can be improved by recycling theby-products and unconverted reactants.

We claim:

1. The process for converting dichlorodifluoromethane to otherfluorinated organic compounds which comprises heating a mixture of thevapors of dichlorodifiuoromethane and a saturated lower aliphatichydrocarbon at a temperature from about 400 C. to about 1000 C.

2. The process for converting dichlorodifluoromethane to otherfluorinated organic compounds which comprises heating a mixture of thevapors of dichlorodifluoromethane and a saturated lower aliphatichydrocarbon in the presence of a metallic, platmum-containing catalystat a temperature from about 400 C. to about 1000 C.

3. The process for converting dichlorodifluoromethane to otherfluorinated organic compounds which comprises heating a mixture of thevapors of dichloroclifiuoromethane and a saturated lower aliphatichydrocarbon in the presence of a metallic copper catalyst at atemperature from about 400 C. to about 1000 C.

4. The process for converting dichlorodifluoromethane to otherfiuorinated organic compounds which comprises heating a mixture of thevapors of dichlorodifiuoromethane and a saturated lower aliphatichydrocarbon at a temperature from about 400 C. to about 1000 C., andrecovering the fiuorinated organic compounds from the resulting mixture.

5. The process for converting dichlorodifiuoromethane to otherfiuorinated organic compounds which comprises heating a mixture ofmethane vapors and dichlorodifluoromethane vapors at a temperature fromabout 400 C. to about 1000 C.

6. The process for converting dichlorodifiuoromethane to otherfiuorinated organic compounds which comprises heating a mixture ofmethane vapors and dichlorodifluoromethane vapors at a temperature fromabout 550 C. to about 850 C.

7. The process for converting dichlorodifiuoromethane to otherfiuorinated organic compounds which comprises heating a mixture ofmethane vapors and dichlorodifluoromethane vapors at a temperature fromabout 550 C. to about 850 C., and recovering a fluorinated compound fromthe group consisting of monochlorodifluoromethane. LI-difiuoroethylene,and monofluor-oethylene.

8. The process for converting clichlorodifluoim methane to otherfluorinated organic compounds which comprises heating a mixture ofmethane vapors and dichlorodifluoromethane vapors at a temperature fromabout 550 C. to about 850 C., in the presence of a metallic,platinum-containing catalyst, and recovering a fiuorinated compound fromthe group consisting of monochlorodifiuoromethane. 1,1-difiuoroethyleneand monofluoroethylene.

9. The process for converting diohlorodifluoromethane to otherfiuorinated organic compounds which comprises heating a mixture ofmethane vapors and dichlorodifiuoromethane vapors at a temperature fromabout 550 C. to about 850 C., in the presence of a metallic coppercatalyst, and recovering a fiuorinated compound from the groupconsisting of monochlorodifluoromethane, 1,1-difiuoroethylene, andmonofluoroethylene.

References Cited in the file of this patent UNITED STATES PATENTS NumberName Date 2,384,821 Downing et al Sept. 18, 1945 2,551,573 Downing et a1May 8, 1951 2,566,807 Padbury et al. Sept. 4, 1951 2,599,631 Harmon June10, 1952 u q- F

1. THE PROCESS FOR CONVERTING DICHLORODIFLUOROMETHANE TO OTHERFLUORINATED ORGANIC COMPOUNDS WHICH COMPRISES HEATING A MIXTURE OF THEVAPORS OF DICHLORODIFLUOROMETHANE AND A SATURATED LOWER ALIPHATICHYDROCARBON AT A TEMPERATURE FROM ABOUT 400* C. TO ABOUT 1000* C.